This invention relates to a method and apparatus for regenerating physically acting organic scrubbing fluids which are laden with sulfur dioxide and/or sulfur trioxide and eventually carbon dioxide during the course of a gas purification procedure.
Exhaust gases produced by the burning of sulfurous fossil fuels contain considerable amounts of sulfur dioxide and sulfur trioxide, both of which are extremely harmful to the environment because of their ability to form sulfurous or sulfuric acid when combined with water. Hence, it is important to remove those components from the exhaust gases before releasing the gases into the atmosphere, especially in power plants where large amounts of exhaust gases are produced.
A known process for removing the components involves scrubbing the exhaust gas with aqueous solutions of alkaline or earth alkaline compounds. Recently, dimethylformamide a physically acting organic scrubbing agent which was previously used for other purposes in gas purification processes, has proved effective in removing the sulfur components. In contrast to the above-mentioned chemically acting scrubbing agents, dimethylformamide has the advantage of relatively easy regeneration because the components which have to be removed merely dissolve themselves therein whereas, in the chemically acting scrubbing agents, the components are bound through a chemical reaction.
Ease of regeneration is important, especially with compounds such as sulfur dioxide or sulfur trioxide, because it decisively influences the simplicity and operation of the exhaust gas scrubbing procedure.
In German patent application DE-OS No. 28 48 721, a process is described for the removal of undesired gaseous components from hot exhaust gases. Sulfur dioxide is absorbed from exhaust gases which occur during the oxidation of carbon-containing fuels by the use of dimethylformamide at temperatures below 0.degree. C. The absorbed sulfur dioxide is removed from the scrubbing fluid at conditions of subatmospheric pressure and temperature of approximately 70.degree. C. Hence, the sump of the regenerating column must be constantly heated. Additionally, this process requires constant attention to avoid hydrolyzing the laden dimethylformamide in the regenerating column. Hydrolysis can occur with high temperatures in the presence of an acid aqueous solution. Gases containing sulfur dioxide and/or sulfur trioxide generally carry along water vapor. Hence, it is possible that small amounts of sulfuric acid will be brought into the regenerating column. To make it possible to work below the range of temperatures at which hydrolysis occurs, the regeneration in the known process is conducted below atmospheric pressures. As a result, the amount of heat which must be supplied to the column sump is reduced. However, a constant supply of energy is needed to maintain the sub-atmospheric pressures.
The known process requires expensive apparatus and large amounts of energy in order to accomplish the regeneration of the laden scrubbing fluid.